Use of recycled plastics for structural building forms

ABSTRACT

Modular plastic structural composites formed from a mixture of (A) high density polyolefin and one or both of: (B) a thermoplastic-coated fiber material, or (C) polystyrene, poly(methyl methacrylate), or a combination thereof. Composites molded in the form of I-Beams and bridges constructed therefrom are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationSer. No. 10/563,883, which was the National Stage filing ofInternational Application No. PCT/US03/22893, filed Jul. 21, 2003, whichclaims priority under 35 U.S.C. §119(e) to U.S. Application No.60/486,205, filed Jul. 8, 2003, the contents of all of which areincorporated herein by reference in their entirety. The presentapplication also claims priority under 35 U.S.C. §119(e) to U.S.Application No. 60/683,115, filed May 19, 2005, the contents of whichare also incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention pertains to new building forms made ofdegradation-resistant composites; structures produced from such novelforms; and related methods of producing and using such forms andstructures.

BACKGROUND OF THE INVENTION

There presently are over 500,000 wooden vehicular bridges in the UnitedStates assembled from chemically treated lumber. An estimated fortypercent of them are in need of repair or replacement.

There are several types of chemically treated lumber such as creosotedlumber and pressure treated lumber. These materials are relativelyinexpensive to make and use, and they are just as versatile as any otherform of wood. They also have enhanced resistance to microbial and fungaldegradation and to water.

However, the increasing popularity of chemically treated lumber has somenegative repercussions that are just now being realized. Chemicallytreating lumber takes a perfectly useable, recyclable, renewableresource and renders it toxic. For example “pressure treated” or “CCA”lumber is treated with very poisonous chromated copper arsenic andcannot be burned. While CCA lumber can be buried, the leaching of toxicchemicals makes such disposal strategies undesirable. The disposal ofcreosoted lumber requires the use of special incinerators. Thesematerials are becoming far more difficult and expensive to dispose ofthan to use. However, because of the long useful life of thesematerials, the economic and environmental impact of chemically treatedlumber is just beginning to be felt.

Structural recycled plastic lumber represents a possible alternative tochemically treated lumber. U.S. Pat. Nos. 6,191,228, 5,951,940,5,916,932, 5,789,477, and 5,298,214 disclose structural recycled plasticlumber composites made from post-consumer and post-industrial plastics,in which polyolefins are blended with polystyrene or a thermoplasticcoated fiber material such as fiberglass. These structural compositespresently enjoy commercial success as replacements for creosotedrailroad ties and other rectangular cross-sectioned materials. Themarket has otherwise been limited for structural recycled plasticlumber, because it is significantly more expensive than treated woodenbeams on an installed cost basis, despite the use of recycled wasteplastics.

This significant cost difference became more evident in the constructionof bridge structures in which pressure-treated wooden beams werereplaced with structural recycled plastic lumber composite beams. Whileas strong as CCA treated wood, the recycled plastic composite beams werenot as stiff, and tended to sag, or “creep.” It was possible tocompensate for this by increasing beam dimensions and using more beamsof rectangular cross-section. However, this just added to the alreadyincreased cost for materials and construction in comparison to treatedlumber.

Structural beams that do not “creep” can also be prepared fromengineering resins such as polycarbonates or ABS. However, these areeven more costly than the structural composites made from recycledplastics. There remains a need for structural materials based onrecycled plastics that are more cost-competitive with treated lumber onan installed cost basis.

BRIEF SUMMARY OF THE INVENTION

It has now been discovered that the immiscible polymer blends of U.S.Pat. Nos. 6,191,228, 5,951,940, 5,916,932, 5,789,477, and 5,298,214 canbe formed into structural shapes that are more cost-efficient thantraditional recycled plastic structural beams with rectangularcross-sections. The structural shapes according to the present inventionare molded as a single integrally-formed article and include modularforms such as I-Beams, T-Beams, C-Beams, and the like, in which one ormore horizontal flanges engage an axially disposed body known in the artof I-Beams as a web. The reduced cross-sectional area of such formsrepresents a significant cost savings in terms of material usage withoutsacrificing mechanical properties. Additional cost savings are obtainedthrough modular construction techniques permitted by the use of suchforms.

Therefore, according to one aspect of the present invention, a modularplastic structural composite is provided having web section disposedalong a horizontal axis and at least one flange section disposed along ahorizontal axis parallel thereto and integrally molded to engage the topor bottom surface of the web section, wherein the composite is formedfrom a mixture of (A) high density polyolefin and (B) athermoplastic-coated fiber material, polystyrene, or a combinationthereof. The high-density polyolefin is preferably high-densitypolyethylene (HDPE). The thermoplastic-coated fiber material ispreferably a thermoplastic-coated carbon, or glass fibers such asfiberglass

Also provided is a modular plastic structural composite comprising a websection disposed along a horizontal axis and at least one flange sectiondisposed along a horizontal axis parallel thereto and integrally moldedto engage the top or bottom surface of said web section, wherein saidcomposite is formed from a mixture of (A) high density polyolefin and(B) a thermoplastic-coated fiber material, poly(methyl methacrylate), ora combination thereof.

The flange dimensions relative to the dimensions of the web sectioncannot be so great to result in buckling of the flange sections upon theapplication of a load. Preferably, the vertical dimension (thickness) ofthe flange section is about one-tenth to about one-half the size of thevertical dimension of the web section without any flange section(s) andthe width dimension of the entire flange section measured perpendicularto the horizontal axis of the flange section is about two to about tentimes the size of the width dimension measured perpendicular to thehorizontal axis of the web section.

Other efficient structural shapes according to the present inventioninclude tongue-in-groove shaped boards that form interlockingassemblies. It has been discovered that interlocking assemblies reducethe required board thickness because of the manner in which the assemblydistributes loads between the interlocked boards. This also represents asignificant cost savings in terms of material usage without sacrificingmechanical properties, with additional cost savings also obtainedthrough the modular construction techniques these forms permit.

Therefore, according to another aspect of the present invention, anessentially planar modular plastic structural composite is providedhaving a grooved side and an integrally molded tongue-forming side, eachperpendicular to the plane of the composite, in which the composite isformed from a mixture of (A) high-density polyolefin and (B) athermoplastic-coated fiber material, polystyrene, or a combinationthereof, wherein the grooved side defines a groove and thetongue-forming side is dimensioned to interlockingly engage a groovehaving the dimensions of the groove defined by the grooved side, and thegrooved side and tongue-forming side are dimensioned so that a pluralityof the essentially planar modular plastic structural composites may beinterlockingly assembled to distribute a load received by one assemblymember among other assembly members.

According to another embodiment of this aspect of the present invention,a modular structural composite is provided in which polystyrene isreplaced with poly(methyl methacrylate) (PMMA). Preferably, at least 90%and, more preferably, all of the polystyrene is replaced withpoly(methyl methacrylate). In one embodiment, the composite includesfrom about 20 to about 65 wt % of a poly(methyl methacrylate) componentcontaining at least about 90 wt % poly(methyl methacrylate) and fromabout 40 to about 80 wt % of a high-density polyolefin componentcontaining at least about 75 wt % high-density polyethylene (HDPE).

Preferred planar modular plastic structural composites have at least onepair of parallel opposing grooved and tongue-forming sides, definingtherebetween a width or length dimension of the composite. Preferredcomposites also have board-like dimensions in which the length dimensionis a matter of design choice and the width dimension is between abouttwo and about ten times the size of the height, or thickness, dimensionof the composite.

The modular plastic structural composites have utility in theconstruction of load-bearing assemblies such as bridges. Therefore,according to yet another aspect of the present invention, a bridge isprovided, constructed from the I-Beams of the present invention, havingat least two pier-supported parallel rows of larger first I-beams, and aplurality of smaller second I-beams disposed parallel to one another andfastened perpendicular to and between two rows of the larger firstI-Beams, wherein the top and bottom surfaces of the second I-Beamflanges are dimensioned to nest within the opening defined by the topand bottom flanges of the first I-Beams.

The distance between the rows of first I-Beams and the rows of secondI-Beams will depend upon factors such as the flange and web dimensions,the plastic components of the composite and the load to be supported bythe bridge. Furthermore, whether the horizontally disposed axes of thefirst or second I-Beams extend in the direction of travel on the bridgeis a matter of design choice, which may in whole or in part depend uponthe aforementioned factors.

Because the second I-Beams are nested within the opening defined by thetop and bottom flanges of the first I-Beams, the top surfaces of thesecond I-Beams are recessed below the top surfaces of the first I-Beamsby a distance that is at least the thickness dimension of the top flangeof the first I-Beam. Bridges constructed according to this aspect of thepresent invention will therefore further include a deck surface fastenedto the first or second I-Beams. Preferred deck surfaces are dimensionedto fit between the top flanges of the parallel rows of the firstI-beams. Even more preferred deck surfaces have a thickness dimensionselected to provide the deck surface with a top surface that isessentially flush with the top surfaces of the parallel rows of firstI-Beams. Other preferred deck surfaces are formed from the essentiallyplanar modular plastic structural composites of the present inventionhaving interlocking grooved and tongue-forming sides'.

The modular components of the present invention permit the constructionof load-bearing assemblies with fewer required fasteners, reducing theinitial bridge cost, as well as the long-term cost of maintaining andreplacing these corrosion-prone components. The plastic compositematerial also outlasts treated wood and requires significantly lessmaintenance than wood over its lifetime, further contributing to costsavings.

Also provided is a composite building material formed from a mixture ofhigh density polyolefin and poly(methyl methacrylate). This material canbe formed into various articles such as railroad ties and structuralsheets.

Further, despite the unpredictability of polymer blending, it has alsobeen discovered that polyolefin and poly(methyl methacrylate) can formimmiscible polymer blends by replacing polystyrene with PMMA. Thisobservation is surprising because there is no way to predict whichplastics will form acceptable immiscible polymer blends with polyolefin.For example, polyvinyl chloride does not form such a blend withpolyolefin.

The polyolefin/PMMA blends of the present invention possess unexpectedproperties. For example, they are stiffer than thepolyolefin/polystyrene blends even though polystyrene and PMMA aloneeach have essentially the same stiffness, as measured by tensilemodulus. It is also surprising that the polyolefin/PMMA blends arenearly as strong as PMMA alone.

The foregoing and other objects, features and advantages of the presentinvention are more readily apparent from the detailed description of thepreferred embodiments set forth below taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-sectional view of an I-Beam according to thepresent invention;

FIG. 2 is a side-view of the I-Beam of FIG. 1, perpendicular to thecross-sectional view;

FIG. 3 depicts a cross-sectional view of a C-Beam according to thepresent invention;

FIG. 4 is a side view of the C-Beam of FIG. 3, perpendicular to thecross-sectional view;

FIG. 5 depicts a cross-sectional view of a T-Beam according to thepresent invention;

FIG. 6 is a bottom view of the T-Beam of FIG. 5;

FIG. 7 depicts a cross-sectional view of tongue and groove deckingpanels according to the present invention;

FIG. 8 depicts a side view of a bridge according to the presentinvention assembled from the I-Beams of the present invention;

FIG. 9 is a top cutaway view of the bridge of FIG. 8;

FIG. 10 is a top cutaway view depicting the perpendicular fastening of asmaller I-Beam according to present invention to a larger I-Beamaccording to the present invention.

FIG. 11 is a plot of log viscosity versus log shear rate comparingextruded composites having various percentages of PMMA;

FIG. 12 is a plot of log viscosity versus percent PMMA for extrudedcomposites;

FIG. 13 a is a heat flow analysis to determine the melting point ofextruded composites upon initial heating;

FIG. 13 b is a heat flow analysis to determine the melting point ofextruded composites following the initial heating shown in FIG. 13 a;

FIG. 13 c is a plot of the melting temperatures of extruded compositesas a function of percent PMMA;

FIG. 13 d is a plot of the heat of fusion of extruded composites as afunction of percent PMMA;

FIG. 14 is a plot of stress versus strain for extruded composites;

FIG. 15 is a plot of modulus as a function of percent PMMA for extrudedcomposites;

FIG. 16 a plot of log modulus versus log time for extruded composites;

FIG. 17 is a series of SEM images of the surface structure of extrudedcomposites;

FIG. 18 is a series of SEM images of the surface structure of a 60/40PMMA/HDPE extruded composite;

FIG. 19 is a plot of peak stress of composites formed via injectionmolding as a function of percent PMMA;

FIG. 20 is a plot of strain at fracture of composites formed viainjection molding as a function of percent PMMA;

FIG. 21 is a plot of stress versus strain for composites formed viainjection molding;

FIG. 22 is a plot of modulus as a function of percent PMMA forcomposites formed via injection molding; and

FIG. 23 is a plot of HDPE phase melting temperature as a function ofpercent PMMA for composites formed via injection molding.

DETAILED DESCRIPTION OF THE INVENTION

The modular plastic structural composites of the present invention areprepared using the co-continuous polymer blend technology disclosed byU.S. Pat. Nos. 5,298,214 and 6,191,228 for blends of a high-densitypolyolefin and polystyrene and by U.S. Pat. No. 5,916,932 for blends ofa high-density polyolefin and thermoplastic-coated fiber materials. Thedisclosures of all three patents are incorporated herein by reference.

As disclosed in U.S. Pat. No. 6,191,228, composite materials may beemployed containing from about 20 to about 50 wt % of a polystyrenecomponent containing at least about 90 wt % polystyrene and from about50 to about 80 wt % of a high-density polyolefin component containing atleast about 75 wt % high-density polyethylene (HDPE). Compositematerials containing about 25 to about 40 wt % of a polystyrenecomponent are preferred, and composite materials containing about 30 toabout 40 wt % of a polystyrene component are even more preferred.Polyolefin components containing at least about 80 wt % HDPE arepreferred, and an HDPE content of at least about 90 wt % is even morepreferred.

The blend technology disclosed in U.S. Pat. No. 6,191,228 can also beemployed in the present invention to formulate composite materialscomprising a poly(methyl methacrylate) component in place of or inaddition to the polystyrene component. Composite materials may beemployed containing a poly(methyl methacrylate) (PMMA) componentcontaining at least 90 wt % PMMA with the balance of the compositematerial being a high-density polyolefin component containing at least75 wt % high-density polyethylene (HDPE). Polyolefin componentscontaining at least about 80 wt % HDPE are preferred, and an HDPEcontent of at least about 90 wt % is even more preferred. The minimumamount of the PMMA component in the blend is that quantity effective toproduce a perceptible increase in melt viscosity. Composite materialscontaining from about 0.1 to about 65 wt % of poly(methyl methacrylate)(PMMA) are preferred. Composite materials containing from about 10 toabout 40 wt % of PMMA are more preferred, and composite materialscontaining from about 20 to about 35 wt % of PMMA are most preferred.

The polyolefin/PMMA blends of the present invention possess unexpectedproperties. For example, they are stiffer than thepolyolefin/polystyrene blends even though polystyrene and PMMA aloneeach have essentially the same stiffness, as measured by tensilemodulus. They are also tougher than the polyolefin/polystyrene blends.“Toughness” is defined as the ability to absorb energy while beingdeformed without fracturing. For example, a bridge made from thepolyolefin/PMMA blend It is also surprising that the polyolefin/PMMAblends are nearly as strong as PMMA alone.

According to the process disclosed by U.S. Pat. No. 5,916,932 thiscomposite may be further blended with thermoplastic-coated fibers havinga minimum length of 0.1 mm so that the finished product contains fromabout 10 to about 80 wt % of the thermoplastic-coated fibers. U.S. Pat.No. 5,916,932 discloses composite materials containing from about 20 toabout 90 wt % of a polymer component that is at least 80 wt % HDPE andfrom about 10 to about 80 wt % of thermoplastic-coated fibers.

The polyolefin-polystyrene composite materials suitable for use with thepresent invention exhibit a compression modulus of at least 170,000 psiand a compression strength of at least 2500 psi. Preferredpolyolefin-polystyrene composite materials exhibit a compression modulusof at least 185,000 psi and a compression strength of at least 3000 psi.More preferred polyolefin-polystyrene composite materials exhibit acompression modulus of at least 200,000 psi and a compression strengthof at least 3500 psi.

Preferred polyolefin-PMMA composite materials suitable for use with thepresent invention exhibit a compression modulus of at least 227,000 psiand a compression strength of at least 3900 psi. The most preferredpolyolefin-PMMA composite materials exhibit a compression modulus of atleast 249,000 psi and a compression strength of at least 4300 psi.

Composite materials containing thermoplastic-coated fibers according tothe present invention exhibit a compression modulus of at least 350,000psi. The compression modulus exhibited by preferred fiber-containingmaterials is at least 400,000 psi. The composite materials containingthermoplastic-coated fibers exhibit a compression strength of at least4000 psi. The compression strength exhibited by preferredfiber-containing materials is at least 5000 psi.

The polyolefin/PMMA blends of the present invention are suitable forcomposite building materials, such as, dimensional lumber. Lumber madefrom these blends can be used as joists, posts, and beams, for example.The toughness of polyolefin/PMMA lumber offers an additional safetyfeature as the material would sag before fracture to provide a warningof possible failure. The thermoplastic fiber-containing polyolefin/PMMAblends are also suitable for the fabrication of railroad ties.

For certain applications such as, for example, railroad ties, it isimportant that the composite building material exhibit some veryspecific properties. For example, the material must be non-water or fuelabsorbent, resistant to degradation and wear, resistant to the typicalrange of temperatures through which train tracks are exposed andnon-conductive. In addition, the railroad ties must meet certainmechanical criteria. For example, the plastic composite railroad tiewill have a compressive modulus of at least about 170,000 psi along thetie's axis. By the term “tie's axis” it is meant the longest axis of therailroad tie. More preferably, the composite building material useful asa railroad tie will have a compressive modulus along the tie's axis ofat least 200,000 psi and even more preferably 225,000 psi. Mostpreferably, when used for railroad ties, the plastic composite materialwill have a compressive modulus of at least about 250,000 psi.

The present invention is particularly well suited for railroad tiesbecause of the different properties exhibited by the composite buildingmaterials along different axes. Because of the highly oriented fibercontent in the direction of the floor (the long axis of a railroad tie),the tie exhibits incredible strength and rigidity along that axis. Atthe same time, in a perpendicular axis which cuts across the orientationof the fiber content, the tie is relatively softer and flexible. Thus, arailroad tie made from the composite building material in accordancewith the present invention will not bend or stress rail laidperpendicularly thereon, as there is some give in that direction.However, because of the strength of the tie along the tie's longestaxis, rails attached thereto will not be allowed to shift laterally orseparate. For this reason, the railroad ties of the present inventionare vastly superior to either wood or concrete ties currently employed.

In addition, in terms of railroad ties, it is important that railsattached thereto not be separated by more than about 0.3175 cm whenplaced under a lateral load of a least about 24,000 lbs. Lateral loadrefers to the outward pressure exerted by the train's wheels on therails. The composite building material should also bear a verticalstatic load of at least about 39,000 lbs. This measures a tie's abilityto stand up to having a train parked on top of it without permanentdeformation, or having the rail driven into the tie. Further, thetoughness of the polyolefin/PMMA material improves the ability of thematerial to accept a spike without fracturing. A vertical dynamic loadof at least 140,000 lbs. is also required. This measures the ability ofa tie to handle train traffic.

Both polyolefin/polystyrene and polyolefin/PMMA blends can also be usedto form the flanged structural members of the present invention. Across-sectional view of an I-Beam 10 according to the present inventionis depicted in FIG. 1, with a side view of the same I-Beam shown in FIG.2. The I-beam has a traditional structure consisting of middle “web” or“body” section 20, an upper flange 30, and a lower flange 40. The flangesections include a protruding section 50 that extends beyond the widthof the web 20. The face of the web 60 forms a structure that can engageother structures (e.g., smaller beams), as described further below. Thewidth A of the flange sections is significantly wider than the width Bof the web section. The height C of the flange sections is smaller thanthe height of the web sections. Despite the thin height of the flangesection and the narrow width of the web section, the I-Beam is capableof supporting heavy structures and can be used in load-bearingstructures, such as bridges and the like.

A cross-sectional view of a C-Beam 12 according to the present inventionis depicted in FIG. 3, with a side view of the same C-Beam shown in FIG.4. The C-beam also has a middle web section 20, an upper flange 30, anda lower flange 40. The flange sections also include a protruding section50 that extends beyond the width of the web 20. The face of the web 60also forms a structure that can engage other structures (e.g., smallerbeams), as described further below.

A cross-sectional view of a T-Beam 15 according to the present inventionis depicted in FIG. 5, with a bottom view of the same T-Beam shown inFIG. 6. The T-beam has a structure consisting of middle web section 20and an upper flange 30, but no lower flange. The flange section alsoincludes a protruding section 50 that extends beyond the width of theweb 20. The face of the web 60 also fauns a structure that can engageother structures (e.g., smaller beams), as described further below.

FIG. 7 shows assembled tongue-and-groove decking panels 100 and 150.Panel 100 includes an end 110 having a tongue-shaped member 120 and anopposite end 130 defining a groove 140. Panel 150 includes an end 160having a tongue-shaped member 170 and an opposite end 180 defining agroove 190. Tongue-shaped member 120 of panel 100 is depictedinterlockingly engaging the groove 190 of panel 150. The groove 140 ofpanel 100 is also capable of interlockingly engaging a tongue-shapedmember of another panel. Likewise, the tongue-shaped member 170 of panel150 is capable of engaging a groove of another panel. Flat top 125 ofpanel 100 and flat top 175 of panel 150 can serve as a load-bearingsurface or barrier when such panels are assembled into a structure.

FIG. 8 illustrates a side view and FIG. 9 a top partial cutaway view ofa portion of a vehicular bridge 200 assembled from the above-describedbuilding forms. In the bridge structure, ends 211 and 212 of respectivelarger I-beam rails 213 and 214 are secured to respective pilings 216and 217 by fasteners (not shown). The opposite respective I-Beam ends220 and 221 are similarly secured to respective pilings 223 and 224.Ends 225, 226 and 227 of smaller joist I-beams 228, 229 and 230 arefastened to the face 260 of I-Beam 213, with respective opposing ends231, 232 and 233 of the three smaller I-Beams fastened to the face 261of I-Beam 214. Similarly, ends 234, 235 and 236 of smaller joist I-beams237, 238 and 239 are fastened to the face 262 of I-Beam 214.

FIG. 10 is a top cutaway view depicting the fastening of end 225 ofsmaller joist I-Beam 228 to the face 260 of larger I-Beam 213 usingL-shaped brackets 243 and 244 and fasteners 245, 246, 247 and 248.Bracket 243 and fasteners 245 and 246 fastening the end 225 of I-Beam228 to face 260 of I-Beam 213 is also shown in FIG. 8. FIG. 8 also showsbracket 247 and fasteners 248 and 249 fastening end 231 of I-Beam 228 toface 261 of I-Beam 214.

FIGS. 8 and 9 also show bridge deck 270 formed from interlocking panels271 and 272 in which tongue 274 of panel 271 interlockingly engagesgroove 275 of panel 272. Tongue 276 of panel 272 interlockingly engagesgroove 277, and so forth. The respective top surfaces 279 and 280 ofpanels 271 and 272 comprise the surface 290 of bridge deck 270.

Suitable fasteners are essentially conventional and include, withoutlimitation, nails, screws, spikes, bolts, and the like.

The molding processes disclosed in U.S. Pat. Nos. 5,298,214, 5,916,932and 6,191,228 may be employed to form the modular plastic structuralcomposite shapes of the present invention. However, because articles arebeing formed having an irregular cross section in comparison to thebeams having rectangular cross-sections that were previously molded, thecomposite blends are preferably extruded into molds from the extruderunder force, for example from about 900 to about 1200 psi, to solidlypack the molds and prevent void formation. Likewise, it may be necessaryto apply force along the horizontal beam axis, for example using ahydraulic cylinder extending the length of the horizontal axis, toremove cooled modular shapes from their molds.

Composite I-Beams of polyolefin and polystyrene according to the presentinvention having a 61 square-inch cross-sectional area exhibit a Momentof Inertia of 900 in⁴. Poly-olefin-polystyrene composite 1-Beamsaccording to the present invention having a 119 square-inchcross-sectional area exhibit a Moment of Inertia of 4628 in⁴. Thisrepresents the largest Moment of Inertia ever produced by anythermoplastic material for any structure, and compares to Moments ofInertial measured between 257 and 425 in⁴ for rectangular cross-sectionwooden beams having a 63 square-inch cross-sectional area and Moments ofInertial measured between 144 and 256 in⁴ for rectangular cross-sectionwooden beams having a 48 square-inch cross-sectional area. The endresult is that a polyolefin-polystyrene composite bridge that would haveweighed 120,000 pounds for the required load rating if prepared fromrectangular cross-section composite materials, weighs just 30,000 poundsinstead when prepared from the I-Beams of the present invention.

Both polyolefin/polystyrene and polyolefin/PMMA blends can also be usedto form structural sheets having a thickness preferably from about ⅛inch to about 1 inch. The length and width of the sheets preferablyindependently range from about 8 inches to about 20 feet. The structuralsheets also have a compression modulus of at least 200,000 psi and astrength of at least 3,000 psi. “Strength” is defined as the higheststress level a material can be subjected to without fracturing intomultiple pieces.

The modular plastic structural composites of the present invention thusrepresent the most cost-effective non-degradable structural materialsprepared to date having good mechanical properties. The presentinvention makes possible the preparation of sub-structures with givenload ratings from quantities of materials reduced to levels heretoforeunknown.

The foregoing description of the preferred embodiment should be taken asillustrating, rather than as limiting, the present invention as definedby the claims. As would be readily appreciated, numerous variations andcombinations of the features set forth above can be utilized withoutdeparting from the present invention as set forth in the claims. Suchvariations are not regarded as a departure from the spirit and scope ofthe invention, and all such variations are intended to be includedwithin the scope of the following claims.

EXAMPLES

The following examples provide representative preparation methods forpolyolefin/PMMA blends according to the present invention.

Example 1 Extrusion

HDPE (CP Chem Marlex HHM-5502BN) and PMMA (Atofina Plexiglass VO45100)were mechanically mixed and melt blended using a Randcastle specialcompounding extruder operating at 180 RPM and 200-210° C. Compositionratios of HDPE/PMMA were: 100/0, 90/10, 80/20, 70/30, 65/35, 60/40,50/50, 40/60, 30/70, 20/80, 10/90, and 0/100.

Rheological tests were conducted to investigate the viscosity of thepelletized extruded composites. As the PMMA content of the extrudedcomposites increases towards neat PMMA, the viscosity of the extrudedcomposites increases (FIG. 11). At both low and high shear rates, anon-linear dependence of viscosity on PMMA concentration was observed(FIG. 12).

Thermal analysis of the extruded composites was conducted to examine themelting temperature and heat of fusion (FIGS. 13 a-d). The heat offusion of the blends approximately correlates to the percentage ofmeltable polyolefin in the blend.

Flexural experiments were conducted to investigate the mechanicalproperties of the extruded composites. Sample diameter ranged from1.18-1.95 mm. The support span was either 20 or 28 mm to maintain a 16:1L:D ratio. FIG. 14 is a plot of stress versus strain for each extrudedcomposite. Table I sets forth the modulus (the ratio of stress to strainin flexural deformation) of the extruded composites according tocomposition:

TABLE I Modulus Standard Deviation Modulus % PMMA % HDPE (MPa) (MPa)(ksi) 0 100 1154 36 167 10 90 1508 94 219 20 80 1916 87 278 30 70 2017104 292 35 65 1689 85 245 40 60 1805 113 262 50 50 2053 269 298 60 402495 250 362 70 30 2667 155 387 80 20 2761 147 400 100 0 3437 104 498The modulus of the extruded composites increases with PMMA content (FIG.15). FIG. 16 is a plot of log modulus as a function of log time, whichshows that the modulus of the blends and the resistance to deformationwith time is increased with increasing PMMA content.

SEM images were obtained to examine the surface structure of theextruded composites (FIG. 17). The composite of 60/40 PMMA/HDPE exhibitsco-continuous morphology (FIG. 18). Co-continuous morphologies have beenknown to exhibit exceptionally high stress transfer between the phases.

Example 2 Injection Molding

HDPE (CP Chem Marlex HHM-5502BN) and PMMA (Atofina Plexiglass VO45100)were mechanically blended and injection molded using a Negri BossiV55-200 Injection Molding Machine. Composites were molded at 392° F.Composition ratios of HDPE/PMMA: 100/0, 90/10, 80/20, 70/30, 65/3560/40, 50/50, and 40/60.

The tensile strength of the blends remains fairly constant in all blendsfrom pure polyolefin up to and including the co-continuous region. (FIG.19). The tensile strain drops as PMMA is blended at higher percentagesto polyolefin in a non-linear manner, but remains much higher than purePMMA itself. (FIG. 20).

The modulus of the blends increases as PMMA is increased, but with lowerstrain to failure and resulting toughness. (FIG. 21). Many of the blendsindicate higher toughness than PMMA or polyolefin alone. Results fromFIG. 21 are summarized in Table II:

TABLE II Width Thickness Modulus Peak Stress % Strain at % PMMA (inches)(inches) (ksi) (ksi) Fracture 0 0.494 0.138 180.682 3.7 73.447 10 0.4950.138 227.439 3.9 50.713 20 0.495 0.137 248.911 4.3 19.046 30 0.4960.138 267.694 4.5 6.716 35 0.496 0.137 284.208 4.5 5.326 40 0.496 0.137294.963 4.4 3.639 50 0.497 0.132 328.982 4.6 2.873 60 0.496 0.135346.735 4.3 2.013

The law of mixtures for modulus is generally followed in the blends,indicating that remarkably good stress transfer between the phases isachieved in this blend system. (FIG. 22). DSC reheat results areprovided in FIG. 23.

The foregoing examples and description of the preferred embodimentsshould be taken as illustrating, rather than as limiting the presentinvention as defined by the claims. As will be readily appreciated,numerous variations and combinations of the features set forth above canbe utilized without departing from the present invention as set forth inthe claims. Such variations are not regarded as a departure from thespirit and script of the invention, and all such variations are intendedto be included within the scope of the following claims.

1.-20. (canceled)
 21. A composite building material comprising a mixtureof high density polyolefin and poly(methyl methacrylate).
 22. Thecomposite building material of claim 21 further comprising one or bothof as thermoplastic-coated fiber Material and polystyrene.
 23. Thecomposite building material of claim 21, wherein said high-densitypolyolefin is high-density polyethylene (HDPE).
 24. The compositebuilding material of claim 22, wherein said thermoplastic-coated fibermaterial is a thermoplastic-coated carbon or glass fiber.
 25. Thecomposite building material of claim 21, wherein said compositecomprises from about 20 to about 65 wt % of a poly(methyl methacrylate)component containing at least about 90 wt % poly(methyl methacrylate)and from about 40 to about 80 wt % of a high-density polyolefincomponent containing at least about 75 wt % high-density polyethylene(HDPE). 26.-31. (canceled)
 32. The composite building material of claim22, wherein said composite comprises from about 20 to about 90 wt % of apolymer component that is at least 80 wt % HDPE and from about 10 toabout 80 wt % of thermoplastic-coated fibers.